Ion heating and magnetohydrodynamic dynamo fluctuations in the reversed-field pinch

Ion temperature measurements, time resolved to 10 μs, have been made in the Madison Symmetric Torus (MST) reversed-field pinch with a five-channel charge-exchange analyzer. The ion temperature, ${\mathit{T}}_{\mathit{i}}$≊300 eV for I=360 kA, increases by as much as 100% during discrete dynamo bursts in MST discharges. Magnetic-field fluctuations in the range 0.5–5 MHz were also measured. Structure in the fluctuation frequency spectrum at the ion cyclotron frequency appears as the bursts terminate, suggesting that the mechanism of ion heating involves the dissipation of dynamo fluctuations at ion gyro-orbit scales.